Supreme leader Ayatollah Ali Khemenei agreed with Putin and said the United States and other Western powers cannot be trusted.

TEHRAN, Nov. 23 (UPI) -- Russian President Vladimir Putin traveled to Iran Monday -- his first trip there in nearly a decade -- and discussed the ongoing conflict in Syria, saying no foreign nation should interfere with Bashar Assad's regime.

Russia and Iran, political allies, are both supportive of Assad's regime and pledged Monday that they will oppose any foreign nation that attempts to "force any form of government upon the Syrian people from the outside, or decide who should rule them."

A Kremlin spokesman said Moscow and Tehran were united against "external attempts to dictate scenarios of political settlement in Syria."

Putin's trip Monday, his first since 2007, was made so the Russian leader could attend a meeting of the Gas Exporting Countries Forum. While in Tehran, Putin met for about 90 minutes with Ayatollah Ali Khamenei -- Iran's Islamic leader.

Chief among those opposed to Assad's government is the United States, which has long backed Syrian rebel fighters and engaged in numerous actions aimed at dethroning him. Recently, though, Washington and Moscow have sided together in the global fight against terrorism.

Russia and the United States have for months been active in combating militants in Syria and continue to share the same anti-terror philosophy in the West Asian nation. Where the nations do not see eye-to-eye, though, is the issue of whether the controversial Assad should be allowed to remain in power.

Friday, the United States and Russia were among the 15 U.N. Security Council voters to support a resolution encouraging all nations to take any measures necessary to defeat Islamic State and al-Qaida terrorists.

Khamenei agreed, asserting that he doesn't believe the Obama administration is trustworthy.

"The Syrian president has gained the majority vote of the Syrian people with different political, religious and tribal views, and the U.S. doesn't have the right to ignore this vote and election," the ayatollah added.

"The Americans have a long-term plot and are trying to dominate Syria and then the whole region," he added.

Khamenei said other than the controversial nuclear agreement this summer, Iran would not negotiate with the United States on any issue.

Putin was also scheduled to meet with Iranian President Hasan Rouhani during the trip. Tuesday, he is scheduled to meet with the king of Jordan -- a U.S. ally -- back in Moscow.

Also Monday, Putin approved an order that eases a Russian ban against supplying nuclear technology to Iran -- and the nations signed several economic deals, including one that will see Russia build multiple power stations in Iran.